Disorder of a liquid

The label liquid crystal seems to be a contradiction in tenns since a crystal cannot be liquid. However, tire tenn refers to a phase fonned between a crystal and a liquid, witli a degree of order intennediate between tire molecular disorder of a liquid and tire regular stmcture of a crystal. Wlrat we mean by order here needs to be defined carefully. The most important property of liquid crystal phases is tliat tire molecules have long-range orientational order. For tliis to be possible tire molecules must be anisotropic, whetlier tliis results from a rodlike or disclike shape. 

The situation in polymers is completely different. In most polymer systems, the degree of molecular order is somewhere iu betweeu the firll positional order of a single crystal and the complete positional disorder of a liquid or a glass. In polymers, ciystalline domains coexist with amorphous regions. Therefore, a semi-ciystalline polymer is in a non-equilibrium situation. 

T. Moses and Y. R. Shen, Pretransitional surface ordering and disordering of a liquid crystal, Phys. Rev. Lett., 67,2033 [1991). 

The heat capacity of a liquid is always greater than the heat capacity of the respective solid because the liquid, having a greater amount of energetic disorder, has a greater entropy according to... 

Despite the difficulty cited, the study of the vibrational spectrum of a liquid is useful to the extent that it is possible to separate intramolecular and inter-molecular modes of motion. It is now well established that the presence of disorder in a system can lead to localization of vibrational modes 28-34>, and that this localization is more pronounced the higher the vibrational frequency. It is also well established that there are low frequency coherent (phonon-like) excitations in a disordered material 35,36) These excitations are, however, heavily damped by virtue of the structural irregularities and the coupling between single molecule diffusive motion and collective motion of groups of atoms. 

A gas has even greater disorder than a liquid because its constituent molecules ot atoms are no longer constrained to be adjacent to each other. Each gas particle moves more or less independently of the other particles. This state is one of near maximum disorder and near maximum entropy. 

Microhardness (MH), has been shown to be a convenient additional technique to detect accurately the ferro to paraelectric phase changes in these copolymers. The increase of MH as a function of VF2 polar sequences observed at room temperature is correlated with the contraction of the p-all-trans unit cell On the other hand, the fast exponential decrease of MH with increasing temperature, observed above Tc, is similar to that obtained for glassy polymers above Tg and suggests the existence of a liquid crystalline state in the high temperature paraelectric phase. This phase is characterized by a disordered sequence of conformational isomers (tg-, tg+, tt) as discussed for Condis crystals [109]. 

LATENT HEAT. Hem tunned by a substance or system without tin accompanying rise in temperature during a change ol state. As examples, the latent heat of fusion is the amount of heat necessary to concert a unit mass of a substance trnin the solid stale to the liquid stale at the same temperature, the pressure being that to allow coexistence of the two phases. A considerable pari of the latent heat arises from the entropy increase consequent on the greater disorder of the liquid state. The latent heat of sublimation is the amount of heat necessary to convert a unit mass of a substance from the solid state to the gaseous stale at (he same temperature, the pressure being that to allow coexistence of the two phases. 

If we want to calculate the entropy of a liquid, a gas, or a solid phase other than the most stable phase at T =0, we have to add in the entropy of all phase transitions between T = 0 and the temperature of interest (Fig. 7.11). Those entropies of transition are calculated from Eq. 5 or 6. For instance, if we wanted the entropy of water at 25°C, we would measure the heat capacity of ice from T = 0 (or as close to it as we can get), up to T = 273.15 K, determine the entropy of fusion at that temperature from the enthalpy of fusion, then measure the heat capacity of liquid water from T = 273.15 K up to T = 298.15 K. Table 7.3 gives selected values of the standard molar entropy, 5m°, the molar entropy of the pure substance at 1 bar. Note that all the values in the table refer to 298 K. They are all positive, which is consistent with all substances being more disordered at 298 K than at T = 0. 

Recent work has supported early observations (e.g. Aggarwal 1976 Hashimoto et al. 1983) of a liquid micellar phase between the BCC micelle phase and the disordered phase. A representative TEM image from a spherical micellar liquid phase is shown in Fig. 2.18. Kinning and Thomas (1984) analysed SANS data obtained by Berney et al. (1982) on PS-PB diblocks and PS/PS-PB blends where the minority (PB) component formed spherical micelles with only liquid-like ordering. The Percus-Yevick model for liquids of hard spheres was used to obtain the interparticle contribution to the scattered intensity (Kinning and Thomas 1984). The ordering of an asymmetric PS-PI diblock was observed by Harkless... 

The vaporization of a liquid to a gas is disfavored by enthalpy (positive AHvap) because energy is required to overcome intermolecular attractions in the liquid. At the same time, however, vaporization is favored by entropy (positive ASvap) because molecular randomness increases when molecules go from a semi-ordered liquid state to a disordered gaseous state. 

In the glassy state the molecular structure is disorderly, and comparable to that of a liquid. This is clearly demonstrated by X-ray diffraction patterns, in which only a diffuse ring is visible, which indicates some short-distance order in contrast to to the sharp reflections found with crystals as a result of long-distance order. 

OO How does the degree of disorder of a gas compare to that of a liquid or a solid Explain your answer. 

Noncrystalline or amorphous (i.e without form) ceramics are supercooled liquids. Liquids flow under their own mass, but they can become very viscous at low temperatures. Very viscous liquids (for example, honey in the winter time) have solid-like behavior although they maintain a disordered structure characteristic of a liquid, i.e they do not undergo a transformation to a crystalline structure Thus, noncrystalline ceramics, i.e glasses, may behave, in many respects, like solids but structurally they are liquids. 

Mesoporous materials of the M41S family with their regular arrays of uniform pore openings and high surface areas have attracted much attention since their first synthesis in 1992 (61), because their properties were expected to open new applications as catalysts and/or adsorbents. These materials are formed by condensation of an amorphous silicate phase in the presence of surfactant molecules (usually ammonium salts with long alkyl chains). However, the chemistry of the steps of the synthesis process is still not fully clear. Ideas put forward so far include (a) condensation of a silicate phase on the surface of a liquid crystalline phase preformed by the surfactant molecules (62) (b) assembly of layers of silicate species in solution followed by puckering of those layers to form hexagonal channels (63) and (c) formation of randomly disordered rod-like micelles with the silicate species... 

For ice Ih, at the melting temperature, Ty =10 s and tj, = 10" s. In contrast, in water, owing to the disorder of the liquid phase the two times are Xy = 2-3x10 s and Td = 1.8x10" s, respectively. The mean lifetime of the hydrogen bond tiq assumes values interme ate between the characteristic time of structure V and structure D (thb = 9x10" s). We aim to describe the dynamic properties of water in structure D, by means of a theory that can account for diffusional phenomena in the different molecular environments to do this we shall have to apply suitable time-average procedures to processes the time scale of which is shorter than Thb-... 

Gelation is the conversion of a liquid to a disordered solid by formation of a network of chemical or physical bonds between the molecules or particles composing the liquid. The liquid precursor is called the sol, and the solid formed from it is the gel. Gels can be as mundane as the epoxy glue used to mend a child s toy, or they can be as sublime as the jellies, meringues, and custards that delight the mavens of haute cuisine. 

Many techniques for the preparation of nanosized materials (sol-gel, thermal treatment of polymeric precursor, electrochemical deposition, atomic layer deposition [ALD], etc.) lead to amorphous or low-crystallinity compounds by quenching of a liquid-state local structure or a very disordered state. At a given temperature, two phenomena can be at the origin of the broadening of the Raman spectrum (1) the loss of periodicity because of the large contribution of surface atoms, and (2) a low crystallinity, that is to say, short-range disorder or bond distortion, hi many cases the exact origin is not obvious and a comparison must be made with TEM. ... 

The disorder of a system is increased if the system produces gaseous products, when the reagents were solids or liquids, or the number of components increases. Conversely, the production of a charged species in a polar solvent reduces the entropy, because it imposes order on the solvent molecules. The effect of a change in entropy is enhanced by raising the temperature. This can be used to control which particular reaction is favoured. 

---